(a) Field of the Invention
This invention relates to employing reactive diluents, such as substituted or unsubstituted benzylic alcohol, preferably alkoxy benzyl alcohol or dibenzyl ether, together with resole resin and/or novolac resin hardening under acid catalysis.
(b) Description of the Prior Art
The hardening of phenolic resoles by the addition of strong acids is well known. Typical strong acids include the following: hydrochloric, sulphuric, phosphoric, trichloroacetic and sulphonic acids either alone or as mixtures thereof. Most often these acids are employed as aqueous solutions at concentrations varying from 20 to 85%. These hardeners normally cause the resoles to harden rapidly even at ambient temperatures of about 16.degree. C. to about 30.degree. C. As discussed below, hardening with strong acids has major limitations, i.e., they are difficult to control, they cannot easily afford extensive ambient temperature stability prior to hardening, they create corrosion problems, and they are very unstable when furfuryl alcohol, a desirable additive for phenolic resins, is employed with the phenolic resin.
According to U.S. Pat. No. 5,317,050 to Gerber, incorporated herein by reference in its entirety, it is known to employ aryl phosphite latent acid catalysts as an alternative to the strong acids. These latent acids provide controlled work time for hardening phenolic resins at ambient temperature and can provide extended work times at ambient temperatures. The phenolic resins are those which are hardenable by strong acids at ambient temperatures. Aryl phosphites are particularly effective hardening agents for both ambient temperature hardening or rapid hardening at relatively modest elevated temperatures, such as those of from about 50.degree. C. to 100.degree. C., or less, such as from 50.degree. C. to 80.degree. C.
U.S. Pat. No. 5,243,015 to Hutchings et al, incorporated herein by reference in its entirety, discloses a thermosetting phenolic resole resin composition, and process for its use, containing a latent catalyst in an amount adequate to cure the resole resin, upon application of heat, at a rate comparable to a rate of cure obtained with the resin using a conventional strong acid under comparable cure conditions. The latent catalyst comprises a salt of an amine selected from a primary amine, a secondary amine, or mixtures thereof, and a strong acid. Typically, the primary or secondary amine is selected from the group consisting of primary and secondary aliphatic, alicyclic, aromatic and heterocyclic amines. The strong acid is selected from the group consisting of sulfonic acids, organic acids and mineral acids. Typically, the sulfonic acid is selected from toluenesulfonic acid, xylenesulfonic acid, phenolsulfonic acid, methanesulfonic acid and mixtures thereof. Preferably, the strong acid has a pKa measured in an aqueous environment of less than about 3.0. Typical primary and secondary aliphatic amines include methylamine, ethylamine, propylamine, butylamine, dimethylamine and diethylamine, 1,3-diaminopropane, 1,2-diaminopropane, ethanolamine, ethylene diamine, butylene diamine, diethylene triamine, 1,2-diaminocyclohexane, cyclohexylamine, piperidine, pyrrolidine or piperazine.
In an alternate embodiment, the composition includes latent acid plus, as an additional ingredient, some strong acid catalyst typically in an amount which is insufficient by itself to cure resole resin at a commercially useful rate. Use of this lower amount of additional strong acid catalyst permits the composition to retain the extended pot life benefits associated with the latent catalyst, but allows the strong acid to act synergistically in combination with the latent catalyst to accelerate the cure rate of the resole resin dramatically.
U.S. Pat. No. 5,378,793 to Orpin, incorporated herein by reference in its entirety, discloses a hardener for producing phenolic resins from phenolic resoles which comprises a partial phosphate ester which is a latent acid. By partial phosphate ester is meant esters that are produced by reacting condensed phosphoric acids with polyols at strictly controlled temperatures with vigorous agitation under vacuum and with control of free acidity, i.e., until constant acidity values are attained. The partial phosphate ester may be used alone or blended with conventional acid hardener such as an aromatic sulphonic acid, e.g., p-toluene sulphonic acid. Use of such blends allows a wide range of variables to control the activity of the hardener and hence allows the optimization of the physical properties of the hardened resoles. Such hardener blends can then be added to phenolic resoles in an amount from 5-15% w/w, preferably from 5-10% w/w of the total formulation. Using such a formulation, it is possible to obtain bulk pot lives of between 30 minutes and 3 hours at ambient temperatures. However, if the temperature is from 60.degree.-80.degree. C., the pot lives will be in the range from 1-10 minutes. When used alone, the partial phosphate esters are provided in an amount sufficient upon hydrolysis to harden the phenolic resin.
The partial phosphate esters give a pot life of at least one hour at ambient temperatures to the resoles. This is sufficient time for the work-up procedures involved in normal preparation of reinforced phenolic resin composites. The partial phosphate esters act as delayed-action hardeners which allow greater flexibility in process control and minimize wastage of resoles due to premature gelation or hardening.
For certain end uses, e.g., for producing reinforced composites such as prepregs or filament windings impregnated with phenolic resins, phenolic resoles need to be hardened in the presence of reinforcing agents which are usually fibers whether woven or non-woven. Examples of woven fibers include those derived from polyamides, asbestos and glass, e.g., glass mats, or glass cloth. Examples of non-woven fibres include those derived from cellulosic fibers, glass and high molecular weight polyesters. After hardening, the reinforced composite comprising the phenolic resin and the reinforcing agent is then post-cured at about 80.degree.-100.degree. C.
Specific examples of processes, for manufacture of reinforced composites, include resin transfer molding (RTM), contact molding and pultrusion. Typical equipment for the manufacture of reinforced composites for filament winding, such as those referred to above, basically comprises a mandrel, an impregnation tank containing the phenolic resin and a hardener. The reinforcing agent, such as glass fibers, are immersed into the phenolic resin/hardener mixture in the tank to impregnate the reinforcing agent with the resin. After impregnation, the fibers are wound on a mandrel, cured and then removed from the mandrel.
In most processes associated with the production of wet resin based reinforced composites, the pot-life or gel-time of the resin being employed is critical in exercising control of the impregnation, cycling, hardening and curing stages of the process. In the case of resoles hardened by strong acids, pot-lives are short, typically of the order of 4-30 minutes, and the process has to be controlled by use of various expedients.
However, during the manufacture of these reinforced composites it is sometimes desirable to accelerate the rate of hardening of the phenolic resin. Thus, it would be desirable to provide additives which increase the rate of acid hardening when such an increase is desired as, for example, in high speed mold production lines.
Conventional resoles when cured, be it thermally or with acid, exhibit brittleness and poor impact resistance. This is a major drawback in many composite applications that use a liquid thermoset. Additives or technology that markedly improves impact resistance with little or no sacrifice in physical properties or fire-smoke-toxics (FST) behavior could accelerate the use of phenolics in composite applications. This represents a multi-billion dollar market with the major industry segments being transportation (about 31%), construction (about 20%), marine (about 13%), and corrosion (about 13%). Thus, it is also desirable to provide polymer products, especially composite materials, having high impact strength. This would provide products that would be rugged and durable. Thus, it would be desirable to provide additives for achieving such impact strength.